The present invention relates to a centrifugal blood pump, used for renal replacement therapy or as a left ventricular assist pump, which employs a magnetic coupling for rotating an impeller and is capable of providing desired flow and pressure rise at a very low xe2x80x9cspecific speedxe2x80x9d.
There are approximately 38,000 kidney patients per year who are in need of donor kidneys, but the supply of donated kidneys is merely approximately 8,000 per year. Accordingly, many of these patients use hemo-dialysis machines for filtering toxins from blood. These machines typically require the dialysis patient to be attached to a machine for approximately three hours three times per week. Obviously, this is very burdensome for the patient, and it is therefore desirable to provide an improved dialysis device which is portable and/or implantable, which eliminates the need to be connected to current large dialysis machines.
Current dialysis machines use a peristaltic pump to provide the needed low flow rate. The peristaltic pump is a positive displacement pump including a roller which pushes the blood through a rubber tube as it rolls along and compresses the tube. The peristaltic pump is very large in size and is therefore less feasible to be portable or implantable due to its size and the limited life expectancy of flexible tubing.
To date, no other centrifugal pump designs are known to provide the needed low flow rate and low head rise for such an application. Accordingly, the goal of the present invention is to address this severe shortage of donor kidneys by providing a small blood pump for a dialysis device which is portable and/or implantable.
The present invention provides a centrifugal pump having a very low specific speed and using a magnetic coupling for pumping the blood in a manner which reduces shear stresses and provides biocompatibility with the blood.
More specifically, the present invention provides a blood pump including a centrifugal impeller for pumping blood and a volute member enclosing the centrifugal impeller within a volute chamber. The centrifugal impeller and volute chamber are configured to provide a specific speed (Ns) of between approximately 500 and 600, wherein
Ns=NQ0.5/H0.75,
where
N=impeller rotative speed
Q=gallons per minute of flow
H=head rise, in feet
Preferably, the impeller includes a plurality of impeller blades having a ratio Rb of approximately 6.75, wherein Rb=Il/Iw, wherein Il is the radial length of the blades and Iw is the axial width of the blades. Of course, this ratio Rb could vary within the scope of the present invention. As the ratio Rb increases, the specific speed decreases. With a ratio Rb of 6.75, the specific speed Ns is 550.
The blood pump includes biocompatible materials to enable implantation. All surfaces of the pump which contact blood are manufactured from titanium 6AL4V ELI alloy. The pump configuration is unique because it is the first centrifugal impeller style pump that was designed specifically for use in a dialysis device.
In addition, the same design philosophy has been used to design a blood pump with a flow capacity of four liters per minute. This higher flow rate blood pump has the potential to be used as a ventricular assist pump for cardiac patients awaiting heart transplant.
Accordingly, one object of the invention is to create a small blood pump for a portable dialysis unit.
A further object is to provide a pump having the required low flow rate and low head rise in a compact design which is biocompatible for use in an implantable dialysis device.
The above objects and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.